// 定义颜色
@mixin color($color, $background_color) {
    color: $color;
    background-color: $background_color;
}
// 定义边框
@mixin border($style, $width, $color) {
    border-style: $style;
    border-width: $width;
    border-color: $color;
}
// 定义描边
@mixin stroke($color) {
    text-shadow: $color 1px 0 0, $color 0 1px 0, $color -1px 0 0, $color 0 -1px 0;
}